Building With Wood English

7/27/2019 Building With Wood English

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Strategies for sustainable construction:

Building with wood in China


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The Chinese Government values highly the culture of buildingsustainably as a national strategy, and sustainable development of

the economy and society saving energy, reducing emissions and

protecting the environment. We are trying to make environmental

protection and conservation the new engine of economic growth.

Premier Wen Jiabao, 13 November 20091

Cover images:

Glulam structure footbridge with wooddeck, Europe

Entertainment park entrance building

with shops, curved structural glulam,

Chengdu, Sichuan province

Single family wood frame community

houses, Beijing

A seismic-safe wood frame

replacement for a brick and concrete

school building destroyed in the

Sichuan earthquake

5-storey apartment building, wood

frame structure, Europe


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1

Introduction


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Building with Wood addresses opportunities for the further use of wood

in construction in China. It is written for the people of the Peoples

Republic of China so that they might assess and discuss these

opportunities, with full recognition of the advantages and the limitations

of wood used in construction.

Building with Wood does not pretend that wood construction offers a

panacea to solve all Chinas construction or housing requirements.Rather, it focuses on areas where wood construction can offer real

benefits to Chinese society at large and to the many individuals and

families who will need comfortable and high performance housing

within their economic means.

As the Chinese government has stated, construction requirements

in coming years will be massive. Over the next decade, an estimated

75 million multiple family housing units will be required to house

the approximately 300 million people expected to migrate into majorurban and adjacent suburban areas. And even more units will be

required to upgrade the housing stock in smaller cities and towns,

and in rural locations.Above: 8-storey wood structure apartment buildings, Europe


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Wood construction can help address these needs, and Building with

Wood explains how this can be accomplished. It points to significant

advantages for wood construction in such areas as energy savings and

total cost at both household and national levels, the inherent resistance

to earthquakes which have devastated parts of China over the last

century, and the major contributions to Chinas environmental

objectives, including potentially substantial reductions of CO2 emissions.

It addresses limitations of wood used in construction, but also and

importantly, debunks misunderstandings about building codes, costs,

fire safety, durability, land use, and deforestation.

Building with Wood is intended to add to the debate on these critical

choices facing China at this pivotal point in its amazing history. This

Introduction provides a synopsis of each of the seven chapters. In that

way, the reader can be guided to pursue his or her particular interest in

wood and wood construction, or read the book in its entirety.

3

Above: 4-storey wood frame apartments, Canada


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This Chapter focuses on both the range of opportunities and the

limitations of building with wood. It notes, as well, certain advantages

over traditional construction systems in China. Wood structures are not

intended to support high rise buildings, although wood is used ascomponents in tall buildings, including infill walls, roof structures, and

other forms of hybrid construction combining concrete and steel

structures with wood.

Japan, Europe, Canada and the United States have a long tradition of

wood construction, and have developed modern wood building into

competitive solutions for the low to mid-rise segment. However, and as

noted in the Chapter, China has a much longer tradition of building with

wood than North America and most likely even longer than Europe.

This Chapter looks to the immediate as well as longer term possibilities

for wood construction in China, including exciting structural forms and

the use of engineered wood products such as glulam beams and

columns. Here, the architectural beauty and warmth of wood, which so

many Chinese have noted, is open to view and on display.

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Buildingwith woodIndex

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This Chapter notes that China is making huge strides in addressing

environmental issues, demonstrating that it can and will lead in

contributing to international objectives. Wood construction can assist

China in making further improvements in its environmentalperformance to benefit Chinese society, and help achieve national and

international priority objectives, with no additional cost.

This Chapter explains how, noting that the use of wood in construction

reduces the impact on the environment in a number or ways. Firstly, as

explained in Chapter 3, standard wood frame buildings are substantially

more energy-efficient than standard concrete, masonry, or steel frame

buildings. This means reduced use of fossil fuels for energy, less CO2

into the atmosphere from burning those fossil fuels, and thereforereduced impact on global warming and climate change. Secondly, the

manufacture and transport of wood products not only require less

energy, but generate significantly fewer air and water pollutants. Thirdly,

wood construction provides the economic incentive to plant forests

which absorb CO2 from the air. The captured carbon makes up close to

half of the mass of the wood and is retained within the wood for the life

of the product.

The magnitude of these environmental benefits can be substantial. ThisChapter provides the details, referring to sophisticated and modern

measuring techniques, such as life cycle analysis and whole life costing.

This Chapter explains why wood buildings are more energy-efficient

than traditional forms of construction now being built in China, and how

standard wood frame buildings can be upgraded for energy performance

at very little incremental cost. It refers to studies and field tests thatprovide evidence for the order of magnitude of these savings.

This Chapter also refers to Chinese government estimates of rapid

growth in energy consumption reaching an estimated 3 billion tonnes of

coal equivalent in 2010, and growing. There are concerns about energy

shortages and the high national cost for the import of energy materials.

Reducing energy requirements is a stated national priority for China.

Because China has the largest construction volume in the world andbecause buildings in China, particularly residential buildings, consume a

large portion of national energy output, choosing wood construction over

traditional systems of construction will make a large contribution to

achieving national goals set out in Chinas Conservation Plan.

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Energyefficiency

Reducing CO2emissions andimproving theenvironment

2

Page 26 Page 38


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This Chapter addresses the cost-competitiveness of wood frame

buildings compared to concrete and steel frame buildings. It explains

why in a number of instances a wood building is less expensive to build

and to operate over the buildings life cycle. It refers to cost comparisonstudies in Europe, North America and China to provide evidence. It also

points to opportunities ahead in China for further cost reduction as

builders and designers become more familiar with wood building

practices and techniques.

The Chapter notes the predominance of wood buildings throughout the

Unites States and Canada and in regions of Europe and Japan because

they have proven cost advantages, as well as performance advantages.

In Europe particularly, new applications of wood in construction areproving to be cost-effective. These include wood roofs and wood infill

walls in concrete structures, and cross laminated timbers for the

structure of mid-rise buildings.

This Chapter explains why wood is safe, both structurally and with

respect to fire safety, and why it is durable indefinitely, providing

correct design and building practices are followed. All these areas

have been subject to extensive research involving Chinese, Europeanand Canadian scientists.

The Chapter notes that wood platform frame construction has

inherently better performance in earthquake zones. This has been

observed in investigations following severe earthquakes, including

those in the Sichuan region in 2008. The Chapter also notes that

fire safety statistics in Europe and North America show that people

are as safe in a code-compliant wood building as in a code-compliant

building constructed from concrete, masonry, or steel.

Page 46 Page 52

Safety anddurability

54

Costefficiency


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This Chapter establishes the linkages between wood construction and

sustainable forestry practices, which include the importance of legal

harvesting and forest renewal. The use of wood products in construction

provides the economic base for forest renewal and sustainabledevelopment. The Chapter describes the benefits to the Chinese

economy from international trade, including trade in wood products.

Whilst the science of forestry began in Europe, and Canada leads in the

percentage of forests certified as sustainable, China leads the world in

plantation forestry. In a matter of decades, forest cover will have

increased from 6 per cent of land mass to approximately 25 per cent.

These accomplishments are truly outstanding and serve as a model for

other forestry nations.

In addition to wood construction, sustainable forest development

provides another area of common interest to strengthen relationships

between China, Europe and Canada.

This Chapter describes the framework of building codes and standards

that regulate wood products and wood construction, and clarifies any

misunderstandings that might exist in the public mind. These

regulations assure life safety, structural integrity and durability,as well as high performance in such areas as energy conservation

and sound control.

These building codes and standards are, for the most part, relatively

new to China, but are based on years of experience and research.

Chinese specialists worked closely with those from Europe and

Canada in their development. Codes continue to evolve to meet new

opportunities and requirements. The overall system of codes is

comprehensive in nature.

Page 62 Page 72

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Sustainableforestry

7

Codes andstandards


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Buildingwith woodBuilding with wood has a Chinese tradition andis proven over the centuries

Wood construction offers solutions for China,including seismic performance and energyconservation

It is popular for single and multi-family housing

And suitable for commercial andpublic buildings

It is appropriate for medium-rise buildingswhich address Chinas wider housing needs

It can be used in combination withconcrete structures to improve newand existing buildings

Structural glulam, with its strong aestheticappeal, is ideal for large span construction

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Using wood in building structures is nothing new - China has been

building with wood for thousands of years. It has been used as a building

material throughout the ages wherever forests grow. And today, the

international timber trade provides countries which do not have

extensive forest resources with wood from sustainable and certified

forestry to build with.

Experience, research and product development have resulted in a rangeof effective building codes and standards.

Building with wood is becoming increasingly popular as countries

round the world seek more sustainable construction; already 70 per

cent of the housing constructed in the developed world use wood frame.

Although concrete and steel are more common construction materials

in China, the government is looking at different solutions, like wood

building, as part of its sustainability strategy. And considerable advances

have been made in the development of the codes and standards required

to ensure safety, structural integrity, and durability (see Chapter 7

Codes and standards).

Building with wood is proven over the centuries

Previous page: Re-roofing of medium-rise apartment building, downtown Beijing

Top left: Traditional Chinese wood houses, Sichuan

Top right: 4-storey wood frame apartment buildings, Canada

Above: Single family villa, wood-frame construction, Europe

Is it OK to build with wood in China? There are many

misunderstandings among consumers, developers, and policy-

making authorities. In fact, wood frame construction has a lot of

advantages. There is a rationale for most countries of the world to

build with wood It is necessary to analyze opportunities and issues

calmly and scientifically, and then move forward to fill this void in

Chinese architecture and construction.

Mr. Zhu Guangian, President, China Timber and Wood Products

Distribution Association, 2010


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Wood has many benefits as a building material. It is naturally beautiful

and widely available. Its low thermal resistance and capacity to insulate

economically provide excellent energy-efficiency. Strong and light, with

exceptional load-bearing capacity, it is easy to handle and transport. It

reduces the need for massive foundations. Fast, flexible and simple to

renovate, it is easy to work with on-site using simple tools, yet ideally

suited to factory pre-fabrication. It is available as solid wood lumber

products, graded to meet performance requirements, or can be

engineered into panels, columns and beams manufactured to meet

precise performance characteristics. Above all, it is a naturally

renewable, organic material that makes a significant contribution to

the reduction of the earths emissions of carbon dioxide.

Wood construction has major advantages in severe seismic zones

because of its light weight and natural flexibility (see Chapter 5 Safety

and durability). Pre-fabrication makes wood buildings even faster to

erect, which is another reason why they are cost-effective. And they are

built to the same code requirements and performance levels of fire

safety and durability as concrete and steel buildings. Chinese national

codes and standards (see Chapter 7 Codes and standards) have been

published to ensure appropriate design and detailing to resist potential

vulnerability to fire, microbial activity and movement due to changes

in moisture.

Wood housing, particularly multiple family units, is consistent with

Chinas land use and zoning policies. And there are different wood

construction systems appropriate for the different needs of urban,suburban and rural districts.

It has many benefits

Above: Wooden roof of Richmond Olympic Oval, Canada

It is practical to build wood frame housing, despite the high Chinese

population density. Wood frame houses are generally low-density,

because of current code restrictions on the number of storeys. As a

result, some may think it is not suitable to build low-density housing in

China, with its large population and limits on land use Japan is one of

the highest population density countries. Its population density is 2.5

times higher than China. Yet, its light wood frame construction and low-

density housing are a high proportion of total housing.

Mr. Zhu Guangian, President, China Timber and

Wood Products Distribution Association, 2010


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Wood frame construction is already being used for housing in China,

from single family dwellings in the suburbs of cities such as Shanghai

and Beijing, to low-cost rural developments where land availability is

not a problem. They have proved cost-competitive and perform well in

comparison with concrete and steel frame housing.

But much more can be done. Wood construction is the solution to other

building requirements in China as well. These include medium-density

multi-storey apartments, small commercial and office buildings,

schools, medical clinics, nursing homes, universities and research

centres, sports arenas and other recreational facilities.

Wood frame construction: low-rise solutions

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Above: Single family wood frame community, Beijing

Right: Semi-detached wood frame house, Sichuan


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Wood can make a contribution to solving Chinas housing shortages

through high density multi-family solutions. While these can take

the form of two or three-storey apartment blocks, the future liesin the higher-rise buildings which are well-proven in Europe and

North America.

They have gained popularity in these regions because of lower building

costs, woods suitability for highly efficient industrial building methods,

better energy-efficiency, better seismic performance and a growing

environmental awareness. And, because of their low weight, multi-

storey wood buildings can be constructed without the need for extensive

pile foundations. This makes it possible to develop sites which wouldpreviously have been impractical.

In China, as of 2009, existing fire codes do not allow wood frame

apartment blocks of four or more storeys. However, this may be an

option for the future, as these codes are often under review and the

scientific experience supports more storeys.

Wood frame construction:medium-rise solutions

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Above and right: 5-storey wood frame apartment building, Europe


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At present, wood frame is used for single family and multi-family homes

of two or three storeys in China. Wood members form a structural

framework which is sheathed with structural wood panels. Foundations

are generally concrete. The floor above can be either wood or a concrete

slab and forms the platform for the next storey. Roof and wall insulation

and water-proof membranes provide energy-efficiency and protection

from moisture. Interiors are usually dry-lined with fire-resistant gypsum

board, and many different materials can be used for external cladding.

Because the structure has multiple wood members, panels, fasteners

and connectors, loads can be carried through a number of alternative

pathways. As a result, wood frame buildings are highly resistant to

sudden failure in earthquakes or high winds.

Wood frame in China

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Above: Multiple living-unit wood frame construction, Sichuan

Left: A typical wall assembly for wood frame construction

Facing page: Multiple living-unit wood frame construction, Sichuan

Sheathing board

Sheathing membrane

Preservative treated

vertical strapping

Rain screen drainagecavity opening

Paper backed lath

Stucco

Perforated casing bead

Insect screen overcavity opening

Metal flashing

Gypsum wall board

Insulation

Wood framing


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Multi-family units are built using the same techniques and under the

same building codes as single family units, and are separated by code-

required fire-rated assemblies. The units generally range in size from100 to 300 square meters.

Multi-storey wood frame buildings are popular in many countries.

Where five and six-storey blocks are now being built, apartments

are generally on a single storey, separated from each other by

fire resistant assemblies. Horizontal stability in these taller buildings

is achieved using engineering design which incorporates bracedwalls and heavy-duty metal connections between assemblies.

Noise is an important consideration, too. Effective solutions are

available to limit sound transmission through floors and walls.


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Hybrid construction: wood frame storeys on concrete structure

Hybrid construction, where wood construction is combined with

concrete and/or steel, is a promising opportunity for the future of China.

This includes the construction of buildings which have the lower storeyor storeys (or parkade) in concrete, to which a light-weight energy-

efficient wood super-structure can be attached.

In Europe and North America, wood frame buildings of up to six or

seven storeys are achieved using a concrete lower storey. And in China,

buildings of up to three wood frame storeys on top of up to four concrete

storeys may soon be accepted.

These hybrids can combine commercial space, such as stores andoffices, in the concrete portion of the building, with housing in the wood

frame part. In some settings, hybrids may be the most practical,

efficient, and cost-effective option.

Left: Light-weight wood frame storeys on multi-storey concrete building, Europe

Above: Multi-family wood frame apartment building on concrete parkade, Canada


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Chinese fire safety codes allow the use of infill wood frame exterior

walls in concrete structures up to six storeys, soon likely to be extended

to seven storeys high for residential, offices, and certain factories and

warehouses. These structures have been built cost-competitively at up

to twenty storeys in northern Europe for a number of years, where

increasingly stringent energy-efficiency requirements are a key driver.

Exterior infill walls are light, as they are designed to take only the load

of their weight and the wind and seismic loads that directly affect them.

They can be pre-fabricated in a factory or built on-site and have verygood insulation characteristics in relation to their thickness, providing

substantially better energy performance than traditional concrete,

masonry or steel construction.

Where wood frame is used for interior walls in concrete and steel

structures as partitions, it provides flexibility of design, including floor

layout, fire safety, sound insulation and renovation. Wood infill partitions

are non-structural, lightweight, and are suitable for a range of interior

finishes. They can also be designed to meet the fire and sound

requirements for apartment partition walls. Wood frame partitions are

approved up to eighteen stories.

Hybrid construction: wood frame walls in concrete structures

Top left: High-rise apartment building using wood frame infill wall panels, Europe

Above: Assembling pre-fabricated wood frame exterior infill wall panels in amulti-storey concrete structure building, Europe

The main benefits of exterior wood infill walls:

Outstanding thermal properties and energy conservation

Reduced wall thickness maximizes usable living space

by a typical 2 per cent

Shorter on-site construction time through pre-fabrication

Reduced foundation load

Improved seismic performance


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Many of the typically concrete medium-rise residential buildings

throughout China have flat roofs that tend to leak and are poorly

insulated for energy conservation and thermal comfort. These existing

roofs can be covered with a pitched wood frame truss roof. This is a

cost-effective way of keeping the rain out, improving the look of the

building and, with additional insulation in the roof cavity, reducing

energy costs. It is also an effective way of delivering a thermally

comfortable attic space for extra accommodation, or of installing

mechanical systems for heating, cooling, and ventilation.

This system is as competitive for installing roof systems on new

concrete structures as for replacing old concrete roof systems.

Hybrid construction: wood frame roofs on concrete structures

Above: Re-roofed apartment buildings with habitable attic, downtown Beijing

Top right: Attic living space, downtown Beijing

Centre right: Installing thermal insulation in wood frame attic living space

Right: Re-roofed apartment buildings, Xu Hui district, Shanghai


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Engineered wood construction: solid wood panels

Solid wood panel structures provide a leading-edge alternative for

six to ten-storey buildings. Although the technology is relatively new

and not yet recognized in Chinese codes, it is widely used across

Europe. The tallest built so far is a nine-storey residential building in

London, England.

Cross-laminated boards are glued together and used to build walls and

joists. Panels are machined in a factory to fine tolerances by computer-

controlled equipment. The panels arrive on site with apertures for doors

and windows, and wiring and plumbing channels already prepared. The

walls can be insulated to provide a high level of energy-efficiency.

Superior load-carrying characteristics, including lateral stability against

wind and seismic forces, as well as excellent fire safety performance,

make cross laminated timbers suitable for medium and even high-rise

buildings. And the amount of timber used means buildings made with

solid wood panels are highly effective carbon stores.

These environmentally-friendly solid wood buildings offer

longer-term opportunities in China, particularly for high density

housing requirements.

Top left: Assembling solid wood panels in multi-storeyapartment building, Europe

Above: 9-storey apartment building with solid wood panelstructure, Europe


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Engineered wood construction: glued laminated timber (glulam)


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In North America and Europe, structural glue laminated timber is widely

used in constructions where span width is an issue and/or the unique

beauty of the wood is to be exploited architecturally. Glulam beams andcolumns have a strong aesthetic appeal, as the structure of a building

can be expressed in the exposed beauty of the wood.

Glue laminated timber engineered wood beams and columns - are

used in homes, schools, sports halls, railway stations, industrial and

commercial buildings, such as shopping centres and expo buildings,

and public buildings, such as museums and concert halls. They are

also used in landscaping and infrastructure applications such as

glulam bridges.

Glulam beams and columns come as standard products, with a variety

of cross-sections and lengths. Custom designed beams and columns

are pre-fabricated according to customer needs and can include curved

shapes and mechanical interfaces to concrete or steel structures etc.

Glulam is a mature technology in Europe, where large span buildings

are still in use after almost 100 years. Modern design methods are

available and national codes design, production, fire - supportingglulam construction in China are to be approved in 2010.

Facing page, top: Entertainment park entrance building in curved structuralglulam, Chengdu, Sichuan province

Facing page, left: Glulam and wood truss shopping mall, Europe

Facing page, right: Swimming pool with structural glulam roof, Beijing

Top right: Entrance to Swedish pavilion in structural glulam,World Expo 2010, Shanghai

Bottom right: New temple with glulam post and beam structure, Zhejiang


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Landscaping

Top: Heavy duty structural glulam road bridge, Europe

Right: Western red cedar landscaping, Canada


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Wood products, treated with the latest environmentally-friendly

preservatives, or using naturally durable wood such as China fir,Western red cedar, or yellow cedar, are used extensively for

landscaping. Whether decking, pathways, fences, retaining walls, or

small structures like storage sheds and gazebos, wood products fit

naturally into many urban and suburban environments, parks and

other recreational projects.

Above: Wood landscaping, Guangzhou

Below left: Wood decking and seating, Pudong, Shanghai

Below right: Glulam structural arch footbridge with wood decking, Shanghai


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The traditional way to construct wood frame buildings in North America

is on-site, particularly when there is labour availability. In Europe, wood

frame assemblies are typically pre-fabricated. Engineered wood

construction, such as glulam, is most commonly erected piece by piece

on-site. In China, almost all wood buildings are currently constructed

on-site. Building materials and structural components are freighted to

the building site and the various assemblies walls, floors, etc. are

framed on-site. The method requires organization and planning on the

building site and measures must be taken to avoid moisture damage tomaterials. On-site construction relies on a skilled work force and, while

much faster than using other materials, is slower than using pre-

fabricated elements.

On-site construction does not require the initial capital costs for plant

and machinery, nor the need to maintain capacity utilization. It is

particularly appropriate where housing volumes are not large, where

labour is reasonably priced and plentiful, and where flexibility and low

overheads are important.

While more capital-intensive, off-site pre-fabrication has the benefit of

controlled factory conditions, less dependence on on-site labour and

faster construction times.

In the case of wood frame construction, only a few days on the buildingsite are needed to assemble a water-tight structure, complete with roof.

The panels can be pre-fabricated with insulation, windows and doors.

Entire units can even be made complete with electricity, water and

waste pipes, kitchens and wet rooms, floors and papered walls.

Wood construction: on-site or prefabrication

Above: On-site construction of new roof on existing apartment building, Beijing

Facing page, left: Pre-fabrication of wood panels, including installation of services

Facing page, right: Production line for pre-fabrication of wood panels


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Pre-fabricated components are relatively light and can be erected

at heights of several storeys using simple lifting equipment,

such as the cranes on the trucks that deliver components to

site. Components may need protection against the elements

to prevent dampness.

The extent of pre-fabrication varies widely between countries and

companies, depending on economic factors. It does require an

up-front investment in plant and equipment which could impose

an uncompetitive burden. While this is essentially the case in

China at present, over the longer term, pre-fabrication may

prove advantageous.


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2

Reducing CO2emissions and

improving the

environmentWood products store the CO2 absorbed bygrowing trees

Substantial reductions of CO2 emissions

can be achieved by substituting wood forother materials

Wood buildings also reduce CO2 emissionsas a result of their energy-efficiency

Life Cycle Assessment demonstrates the lowenvironmental impact of wood buildings

Whole Life Costing demonstrates the cost-efficiency of wood buildings

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Growing trees absorb CO


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Wood is an extraordinary natural resource. It provides a high-

performance building material without depleting the earths resources.

It grows in forests and plantations which clean the air, creating the

conditions that make the planet habitable, while providing a natural

habitat for leisure and wildlife.

On average, trees absorb one

tonne of CO2

and release

almost three-quarters of a

tonne of oxygen for every

cubic metres growth. The CO2

is stored in the wood as

carbon. Young, active trees

replace the mature trees,

absorbing yet more CO2.

Above: Growing trees absorb carbon dioxide and release oxygen2

Growing trees absorb CO2

Wood plays a major role in

combating climate change.

Trees reduce CO2

in the atmosphere,

since one cubic metre of wood

absorbs around one tonne of CO2.

Greater use of wood in construction

can reduce greenhouse gas

emissions by stimulating the

expansion of Chinas forests and by

reducing requirements for fossil

fuel-intensive products.

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Coping with climate change should be a major strategy fornational economic and social development There should be

greater public awareness in addressing global climate change

and encouraging low-carbon life styles and consumption.

State Council, Press Statement, 27 November, 2009

Wood products store CO2


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Throughout their life, wood products continue to store the carbon

sequestered by the harvested trees. Further CO2 gains can be achievedby extending the life of the wood product, by recycling into panel

products, and by recovering the energy in the wood at the end of its life

by using it as a biomass fuel.

Managing a forest sustainably means ensuring new trees replace the

harvested trees. So the forest maintains its carbon store. And theamount of carbon stored in the product made from the harvested wood

is a net gain. This means the wood can be described as carbon

negative it stores more carbon than the equivalent CO2 it emits from

the harvesting, processing, transport and fabrication. This helps reduce

the growth of CO2 in the atmosphere, slowing down climate change.

Wood products store CO2

Since wood products store the carbon initially trapped in trees,

carbon is removed from the atmosphere for as long as the wood

product remains in use, and beyond, when the product is re-used

or recycled for secondary material or energy recovery.

European Commissions DG Enterprise3

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China is going to reduce the intensity of carbon dioxide emissions

per unit of GDP in 2020 by 40 to 45 per cent compared with the

level of 2005 Appropriate handling of the climate change issue is

of vital interest to China's social and economic development and

people's fundamental interests, as well as the welfare of all the

people in the world and the world's long-term development.

State Council, Press Statement, 27 November 2009

Substituting wood for other materials reduces CO2 emissions


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Using wood in construction is a good thing in itself. Its effects are

even more positive when the CO2 savings made by not using other

construction materials are taken into account.

Wood has lower CO2 emissions than any other building material.

The wood industry is also one of the biggest users of biomass energy,

often contributing excess energy to national grid networks. Even the

recycling of materials such as steel and aluminium, whilst a necessary

part of modern materials production, requires large energy inputscompared with wood.

CO2 emissions will vary by

country, according to the

predominant energy source.

Chinas energy production is

heavily dependent on coal,

which produces high levels

of CO2 emissions.

Substituting wood for other materials reduces CO2 emissions

Substituting a cubic metre of wood

for other construction materials

(concrete, blocks or bricks) results

in an average saving of 0.7 to 1.1

tonne of CO2.2

30

The index of carbon dioxide emissions cuts, announced for the

first time by China, would be a binding goal to be

incorporated into China's medium and long-term national

social and economic development plans Given the country's

huge population, prominent economic structural problems,

coal-dominated energy consumption structure, and increasing

demand for energy, the government needs to make strenuous

efforts to realize those targets.

State Council, Press Statement, 27 November 2009

Lumber (kiln dried)

Steel girders

Concrete columnsand beams

Injectionmoulded PVC

Roofing tiles

-1,000 -500 0 500 1,000 1,500 2,000 2,500

Kilograms CO2 per tonne

Above: Cradle to gate carbon footprints for materials used in construction,Edinburgh Centre for Carbon Management2

Wood buildings have lower CO2


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Saving CO2 emissions from the construction phase is just one part of

the story. At the moment around two-thirds of a buildings CO2emissions come from the in-use phase. Because of woods naturally

low thermal conductivity and the capacity for low cost, effective

insulation, wood construction provides a competitive way to achieve

higher energy-efficiency. As the walls do not have to be so thick to

achieve good insulation, houses built using wood have more livable

space (see Chapter 3 Energy-efficiency).

g 2emissions throughout their lifetime

Besides, the more wood products replace other materials, themore the so-called substitution effect further reduces CO2 in

the atmosphere.

European Commissions DG Enterprise3

31

Right: Zero carbon demonstration house, Europe

Below: Wood frame apartment building, Europe

Life Cycle Assessment shows wood building elements have lower impacts


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Governments world-wide are increasingly concerned about issues like

recycling, waste disposal, and the environmental impacts of materials

production, as well as energy emissions. As a result, buildingregulations internationally are requiring that principles of sustainable

development apply to construction. In some cases these standards are

mandatory. This has led to demands for materials and products to be

assessed over a complete life cycle.

Life Cycle Assessment (LCA) is a tool which assesses the environmental

impacts of a building component right the way through its lifecycle in

three phases:

It helps designers, clients, specifiers and developers understand the full

environmental impact of the materials they choose. It gives them the

information they need to choose materials which will contribute towards

more sustainable buildings.

32

y g p

LCA has been widely used to compare the

environmental impacts of building materials such as

wood, steel and concrete, and scientists world-wide

have come to the same conclusion: compared to the

alternatives, wood buildings produce less air and water

pollution, require less energy across their life cycle, and

generate lower CO2 emissions.

Left: Wood frame structure apartment building, Europe

Production phase

Extraction

Production

Transport to site

Construction

In-use phase

Energy use

Thermal properties

Maintenance

End-of-life phase

Recycling

Recovery

Disposal

Whole Life Costing shows how competitive wood solutions can be


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Whole Life Costing (WLC) is a commonly used technique which assesses

the cost of a product or project over a specific period of time. It takes

into account all relevant financial factors from the initial capital costs,

through future operational costs, to disposal.

WLC, together with LCA, can provide a thorough economic and

environmental assessment to support decision-making and an effective

procurement strategy.

g

Right: Glulam construction for rapid transit system, Canada

Below: 8-storey apartment building, glued solid wood structure, Europe

Case studies of the CO2 emissions savings to be made by using wood


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Example 1: A solid wood panel school building

The more wood used in a building, the lower its carbon footprint. This

school uses solid timber as its primary structure to achieve a negative

materials footprint of -40.9 tonnes of CO2.4

Example 2: Two multi-storey apartment blocks

Research in Sweden in 2007 compared the CO2 balances for two four-

storey buildings, one with a timber frame and the other with a concrete

frame, over a 100-year period.5

The study researched the entire construction process from cradle to

grave. A 4-storey wood framed building with 16 apartments (1,190 m2

area) was compared with a similar concrete frame construction. The

concrete frame building showed emissions of around 96 tonnes of CO2,

while the timber frame building showed no emissions - instead it

showed a net uptake of 150 tonnes of CO2.

- The construction of the building with the wooden frame

required less energy

- Wood waste from the construction process could be

recycled and used as an alternative to fossil fuels

- Carbon from CO2 emissions is stored in the wood

- Concrete production has significant CO2 emissions

- The more wood used to replace steel and concrete,

the better for the climate.

34

Above: Low carbon demonstration school building using solid woodpanel construction

Facing page left: The wood frame apartment building in the Swedish carbondioxide comparison study

Facing page right: A low carbon apartment building under construction usingsolid wood panels, Europe

Emissions of around 96 tonnes of CO2 from the concrete buildingcompared with a net uptake of 150 tonnes of CO2 from the timberframe building

Wood frame building Concrete building


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Example 3: A solid wood panel multi-storey apartment block

This apartment building in London has a solid wood structure. It was

pre-fabricated offsite using laminated panels up to 12.5m long, 2.9m

wide and 170mm thick, produced from sawmill offcuts.

The glue content of the panels is 2 per cent and the building uses 360m3

of lumber, saving around 400 tonnes of CO2 emissions compared with a

concrete and steel construction.4

35

LCA case studies


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36

Example 1: Wood versus steel, and wood versus concrete, a study

of single family homes in the USA6

A study by the Athena Institute, Canada, looked at the environmental

impacts of wood compared with steel and concrete in single family

homes in Minnesota and Atlanta, USA. Results showed considerable

benefits for wood construction in both instances, across a range

of environmental impacts, including air and water pollution and

solid waste.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Embodiedenergy (Gj)

Global warmingpotential Equiv.

CO2 (kg)

Air pollution(index)

Water pollution

(index)

Solid wastes (kg)

Embodied

energy (Gj)

Global warmingpotential Equiv.

CO2 (kg)

Air pollution(index)

Water pollution

(index)

Solid wastes (kg)

0 1 2 3 4 5 6 7 8 9 10

Wood

Steel

Wood

Concrete

Environmental impacts of wood house vs steel house

Environmental impacts of wood house vs concrete house


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Example 2: A comparison of wood, steel and concrete apartment

construction in China7

A study carried out by Beijing University of Technology (BJUT) compared

the life cycle performance of similar wood, steel and concrete

apartment buildings over a 50-year service life. The study focused on

the production and in-use phases. The LCA considered all energy and

material flows from the environment, as well as emissions to air, water

and ground from the three building designs.

The findings showed the wood frame construction was about 25 per cent

more energy-efficient than either the steel or concrete frame designs

across the overall life cycle. They demonstrated the importance of the

energy embodied in materials (the production phase), even compared

with the long-term operating energy consumption. And they highlighted

the importance of improving building insulation levels, air tightness and

other energy conservation measures.

Example 3: An exploratory study of Energy Use and Environmental

Impacts of Wood Frame Structures Relative to Other Structures

in China8

A second study compared the environmental impacts of three different

construction systems, wood frame, steel frame and concrete frame,

using three houses of the same footprint (223m2) and total floor area

(607.8m2). To simplify the data, the study considered the impacts of six

main building materials within each house: cement, steel, timber,

glazing, OSB and I-joists.

From the table it can be clearly seen that the wood frame construction

produces the least damage to the ecosystem, and consumes the least

resources (except for timber, which is, of course, renewable).

Embodiedmaterials

Construction

Use andOperation

WholeLife Cycle

Woodstructure

Steelstructure

Concrete

structure

Wood Frame Construction

Steel Frame Construction

Concrete Frame Construction

Ecosystem damage

Resource consumption

Total

The energy consumption for each phase and life cycle ofthree types of building

Ecosystem damage and resource consumption


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Energy-efficiencyChina needs increasing energy supplies

But most energy production has an impacton the environment

Energy-efficient buildings are part ofthe answer

Wood buildings are more energy-efficient

Wood frame buildings are easier to insulate

Research confirms wood buildings save energy

They outperform Chinese energy codes

And reduce the cost of meeting the codes339

China is facing an energy challenge


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40

China is experiencing rapid economic development. It has the worlds

second largest energy consumption, exceeded only by the USA. In 2003

its total energy consumption was 1.68 billion tonnes coal equivalent. By

2010, according to a recent government estimate, energy consumption

could exceed 3 billion tonnes a year.9

This growth in consumption has led to energy shortages, which can hold

back economic development. And, in spite of extensive domestic fossil

fuel reserves, China has become one of the largest energy importers in

the world.

Improving energy-efficiency and developing renewable energy supplies

have therefore become a priority.

Energy production has a serious impact on the environment

Chinas current energy supplies are heavily dependent on fossil fuels,

which emit large quantities of CO2. Rapid economic development,

accompanied by higher energy consumption and the use of fossil

fuels, is presenting serious challenges to air and water quality

across the country.

Improving energy conservation and using environmentally friendly and

renewable materials can reduce the impact of economic development

and provide a better living environment for Chinas population.

Left: Energy-efficient wood frame infill wall installation in a concretestructure building

Facing page: Energy-efficient wood frame ski lodges, Xiliang mountain, Sichuan

The energy consumption of buildings takes about 28 per cent

of the total energy consumption in China, but it is expected toincrease in the coming years. However, most urban buildings

are expected to be retrofitted by 2020 in order to improve

energy efficiency.

Deputy Minister Qiu Baoxing, Ministry of

Housing and Urban Rural Development11

It is important for fast growing economies to promote energy

savings in new building development and green buildings,

and to renovate existing buildings using green and energy-saving technologies.

Deputy Minister Qiu Baoxing, Ministry of

Housing and Urban-Rural Development10

Energy-efficient buildings are vital to Chinas development


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The construction and operation of buildings create greater

environmental impacts than most people realize. Globally, buildings are

responsible for 20 per cent of all water consumption, 25 to 40 per cent

of all energy use, 30 to 40 per cent of greenhouse gas emissions and 30to 40 per cent of solid waste generation. 12

Estimates suggests that the building sector now accounts for about

one-third of Chinas total energy use, and this is expected to grow in

the future.13

The residential sector accounts for about 38 per cent of total building

energy use, a proportion that is likely to continue to rise along with

increasing affluence and urbanisation.14

It is important to consider the scale of Chinas construction and the pace

of change. China has the largest construction volume in the world.

Almost two billion square metres of new buildings are completed each

year. Although more than 80 per cent of buildings are categorized as

energy-inefficient, with energy consumption per unit area currently two

to three times higher than in developed countries, China has set

ambitious targets and will work hard to achieve them.15

According to Jiang Yi, professor in architecture at Tsinghua University,

energy use in the building sector will double by 2020 if no serious

action is taken.15

Using wood in buildings is an important step towards meeting

these demands.

Global construction spending 2007 (US$bn)16

Global construction spending growth 2008 (% change)16

0 200 400 600 800 1000

USA

Japan

China

Germany

Italy

France

UK

Brazil

Spain

Korea

Mexico

Australia

India

Other

-2 0 2 4 6 8 10

USA

Japan

China

Germany

Italy

France

UK

Brazil

Spain

Korea

MexicoAustralia

India

Other

The government has implemented energy-efficiency measures


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42

There are two sets of national building energy standards in China,

one for public buildings and another for residential buildings. Both

standards are set as mandatory by MOC, and China is addressing the

challenges of enforcement. In 2005, MOHURD (the Ministry of Housing

and Urban-Rural Development) began a building inspection programme

to monitor the implementation of building energy-efficiency. Under

this programme, design institutions, developers and construction

companies will lose their licenses or certificates if they do not comply

with the regulations.

In November 2004, the National Development and Reform Commission

(NDRC) issued the China Medium and Long Term Energy Conservation

Plan (Conservation Plan), which stressed energy conservation as the key

principle for sustainable socio-economic development in China and an

urgent issue to address. In the Conservation Plan, energy saving targets

for buildings have been emphasized:

- During the Eleventh Five-year Plan period, new buildings should be

subject to a strict 50 per cent energy-saving design standard. Several

major cities, such as Beijing and Tianjin will go further, implementing

a 65 per cent energy-saving standard

- Existing residential and public buildings will be subject to energy-

saving retrofit measures as part of urban reconstruction. Large cities

are expected to improve 25 per cent of building areas, medium cities

15 per cent and small cities 10 per cent.

Top: Wood construction office building, Shanghai

Wood buildings are more energy-efficient


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Wood construction consumes minimal energy. Wood is light and easy to

put together on site. Foundations are minimized. Transport requires less

energy. And wood construction is quick, requiring little or no use of

heavy-duty equipment.

Wood is a good thermal insulator. It is 400 times better at resisting

thermal conductivity than steel, and 10 times better than concrete or

bricks. This means extra insulation or thicker walls are required for

steel, concrete, or masonry structures to achieve the same level of

thermal resistance.

Tsinghua University investigated the energy conservation

performance of wood construction using standard building

techniques with comparable concrete and steel

construction. The wood buildings generally out-performed

both concrete and steel.

Professor Lin Borong, Tsinghua University, March 2010

Above: Wood frame construction provides thermal comfort

Right: Thermal insulation in the cavities of an exterior wood frame wall reduceswall thickness and maximises usable living space by two to five per cent

Wood frame buildings are easy to insulate thermally


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Unlike solid concrete or masonry structures, wood frame walls, floor

joists, and roof joists inherently provide space for fibrous insulation, the

most economical way to achieve better insulation. Application of mineral

insulation is a standard element of any wood construction project. It is

conducted with minimal additional labour or material expense and

provides significant returns. Woods low thermal conductivity means 90per cent of the insulation value can be realized, with only 10 per cent

lost to thermal bridging. Wood structures can also be readily insulated

on the exterior or interior if additional energy savings are desired.

Light steel frame walls also have cavities for insulation. But the high

thermal conductivity of steel means only 50 per cent of the insulation

value can be achieved. Extra measures are always required to reduce

local energy loss and vapour condensation as a result of steel thermal

bridging. It can also lead to ghost marks; dark vertical marks thatappear over the framing on the interior surfaces of exterior walls, as a

result of faster dust accumulation on cool surfaces.

An energy consumption field test by the Harbin Institute of

Technology considered a wood building using 38 mm x 140 mm

studs, cavity insulation and 30 mm of exterior rigid panel polystyrene

insulation. This was compared with a brick building clad with 60 mm

rigid panel polystyrene insulation. Harbin is an area which experiences

severe cold.17

The test measured the thermal transfer coefficients (K) of the walls

as 0.244 for wood buildings and 0.526 for brick buildings. The timber

building reduced coal consumption by about 50 per cent.

Above: Insulation is simple to fit in wood buildings

Facing page: Infra-red temperature imaging of exterior wall

Field tests in China confirm wood buildings save energy


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Wood frame construction outperforms Chinese Energy Codes with no

additional cost

Wood frame buildings are generally rated as more efficient and

economical than other construction types. They outperform all the

relevant requirements for building energy efficiency in China with no

additional cost.

JGJ 26 Standards for Energy Design for Severe Cold and Cold Areas

requires buildings in Beijing to have thermal transfer coefficients (K)

from 0.55 to 1.16. Typical wood frame walls can achieve thermal transfer

coefficients from 0.3 to 0.5 depending on stud size, spacing and

insulation materials.

According to calculations by Shanghai Xiandai Architectural Design

Group, the effective thermal transfer coefficients of conventional

wall assemblies with 38 mm x 89 mm studs, range from 0.46-0.49

and 0.37-0.40 with rock wool and glass fibre insulation, taking into

account the thermal conductivity of the studs. These thermal transfer

coefficients (K) can be further reduced to 0.3 or lower if 38 mm x 140

mm or wider studs are used for framing, or extra exterior insulation is

applied. By comparison, steel, concrete, or brick walls would requireextra and more expensive, rigid insulation panels in order to achieve

similar insulation performance, and walls would be thicker.

The energy-efficiency of wood construction reduces the cost of

meeting the codes

All concrete, masonry, and steel frame structures need rigid insulation

panels in order to meet Chinas energy efficiency requirements. In

Beijing, concrete or masonry buildings need additional 50 mm to 80 mm

thick insulating panels. In Shanghai, they need 50 mm thick panels in

order to meet the minimum energy requirements. By comparison,

conventional wood frame construction using fibre insulation meets the

requirements without additional insulation, using 38 x140 mm studs inBeijing and 38 x 89 mm studs in Shanghai. A considerable saving can

therefore be made.

If additional insulation is not used, steel and concrete buildings will

consume much more heating and cooling energy. The savings in cooling

and heating costs of wood frame building envelopes have been

confirmed and praised by developers and property managers who have

experience with these constructions in China. As one of the worlds

largest countries, China is subject to extreme climate variations. Theenergy-efficiency of wood structures is beneficial in all climates, but

particularly in Chinas colder regions, where heating is required.

Thermal conductivityis the rate of heat transferred by conduction through solid materials

subject to a temperature difference on each side of the material.

Thermal transfer coefficient(U-value or K-coefficient) is a measure of heat conductivity

through a building assembly, comprising a number of materials.

Thermal resistance(RSI) refers to the resistance to conductive heat transfer through a

material or assembly. It is the reciprocal of conductivity (1/K).

A lower Kor a higher RSI means better thermal or insulating performance.

Thermal bridgingrefers to the higher thermal conductivity of a structural component,

within the insulated assembly, providing a bridge for more rapid heat transfer through the

assembly and thereby reducing the overall thermal performance of the assembly.


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47

Cost-efficiencyWood frame is popular world-wide

There are many studies showing it is cost-

efficient in construction and operation

Studies in China show it can be cost-effective

across many segments, including commercial,

recreational, and residential

Particularly when high energy-efficiency andseismic safety are required

As building with wood becomes more popular

in China, costs will become even more

competitive4

The most popular system in the developed world


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It is never easy to compare the costs of building with different materials

and systems. So many factors are involved. For example, the relative

costs of different materials change according to supply and demand as

well as currency fluctuations. Local conditions vary significantly. And

there are many different ways to build in different materials. Building

with wood could involve anything from traditional wood frame, to

technologically advanced engineered systems, or even hybrid

construction. And building efficiencies vary, depending on the regulatory

system, scale of development, knowledge and skills, the extent of off-

site construction, and how adept and experienced the construction

company is at planning and managing the building process.

It is worth noting, however, that wood frame systems account for around

70 per cent of residential construction in the developed world. And 90

per cent in North America. One of the reasons for its popularity is its

cost-effectiveness, which includes a much shorter construction time and

less waste than other systems.

48

Wood frame construction (WFC) products and components are

manufactured in a factory, which means higher construction

efficiency, shorter construction period, lower cost, quicker

capital turnover. It takes around 100 days to build a 300 m2

single family residence with WFC, while a concrete building

needs around 145 days. Also, wood houses are light. The dead

weight of WFC walls is only about 1/10 of concrete walls, and

the dead weight of WFC floors and roofs is about 1/8 of the

concrete ones. So WFC has much lower requirements on

foundations, which is cost-saving.

Mr. Zhu Guangqian, President, China Timber and

Wood Products Distribution Association, 2010

Cost-competitive world-wide


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International comparisons show cost advantages for building with wood

over concrete and steel for many types of residential and commercial

buildings. These demonstrate the potential for cost savings in China

from building with wood, recognizing that modern wood construction in

China is new and full economies have yet to be realized.

One study, carried out in South Carolina, USA, showed wood frame

houses saving 14 per cent in construction costs compared with

identical steel frame houses.18

A recent cost study comparing wood and concrete for the construction

of a three-storey motel building in the United States demonstrates

that using wood can achieve a saving of 7-9 per cent in material

costs alone.19

Experiences in Europe demonstrate that wood construction can cut

costs substantially, depending on design and application. If off-site

pre-fabrication is used, construction time can be reduced by as much

as two-thirds, compared with other construction types.

Even in areas like Taiwan, where wood frame construction is still

relatively new, it has been shown by local design professionals that

wood construction can be cost-competitive with concrete buildings.

Wood roofs were shown to be less expensive than concrete roofs.20

As wood is a better thermal insulator than other structural materials,

wood frame buildings reach the high insulation standards increasingly

demanded by governments world-wide more easily.

There is also the additional benefit of a two to five per cent increase inliving space, as the wood frame walls can achieve excellent insulation

values with a substantially thinner cross-section than other materials.

This is a significant cost advantage on the basis of liveable space, which

is generally not taken into account in standard cost comparisons.

Research in the United Kingdom shows that wood frame construction

becomes even more cost-competitive when higher energy-efficiency

building envelopes are required.21

Above: 6-storey wood construction apartment buildings, Europe

Facing page: Wood frame apartment building, Canada

90 95 100 105 110 115

Cost comparison between wood and concrete construction

for three-storey buildings in the USA19

Concrete Wood

Cost-competitive in China


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Although modern wood construction is new to China, with full cost

savings yet to be realized, in-depth research shows that wood frame

construction is competitive depending on its application.

For example, a cost comparison study was conducted in China looking

at identical building designs constructed with different structural

materials. The results showed the construction costs of wood frame

houses without living space in the lofts were lower than for concrete

or masonry. In particular, materials and cost savings could be made in

the foundations. When living spaces were built into the lofts, the cost

of wood frame could be higher. But when comparisons are made per

square metre of living space, they still work out cheaper to build than

comparable concrete houses.

The study also demonstrated that wood roofs can be cost-competitive

with concrete roofs, as well as having better thermal, seismic and

occupant comfort performance.

Wood frame houses are promising for rural areas

Research has shown that small-scale rural wood frame houses can

be built for about 1000 RMB per square metre.22 This is affordable for a

large percentage of the population in rural China. Construction of such a

new building system to replace traditional masonry and concrete houses

would improve occupant comfort, thermal performance and seismic

safety. It would be an important signal of improved living standards for

Chinas large rural population.

Wood infill walls could revolutionize high-rise construction

European experiences with non-load-bearing wood infill walls in

concrete high-rise buildings suggest they would be cost-competitive

in China. Combining wood with concrete could revolutionize high-rise

construction in China, with cost advantages, lighter weight, better

thermal and seismic performance, and environmental benefits.

Wood construction could make a significant contribution to Chinas

green revolution.

50

Above: Wood frame house used for comparative energy study by Harbin

Institute of Technology

Wood frame construction (WFC) is considered by some to be

expensive. I have to explain this: In China at the present time

WFC is usually designed for villas with foreign housing

finish which is even more luxurious than our domestic high-

end finish. So the costs can get high. Changing the standard

of finishes, designing for low to middle-income people andlocalizing the production of materials, are certain to bring

costs down.

Mr. Zhu Guangqian, President, China Timber and Wood

Products Distribution Association, 2010


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Wood construction costs are becoming even more competitive in China

Wood construction costs in China are continuing to decline in

comparison with traditional construction. This is as a result of the

introduction and revision of building codes and standards, more

extensive training for design, construction and maintenance,

more building experience, new building methodologies and larger

scale construction.

Continuing cooperation between China and Europe and Canada in code

development, quality issues, cost-saving building techniques, training

and skill development, and research will accelerate improvements in

cost performance.

It is important that wood frame buildings are correctly and appropriately

designed and constructed to achieve their full efficiency and cost-saving

potential. On balance, any meaningful comparison of competitiveness

must move beyond costs alone into a broader evaluation of all the major

performance attributes, where wood construction outperforms

traditional construction in many other respects.

51

Above: Wood frame replacement housing Qingchuan county, Sichuan

Right: Light-weight wood frame storeys can be added to new or existing

multi-storey concrete buildings

While modern wood construction in China is very recent, there

is evidence that the overall cost of wood buildings, when

considered over the full life cycle, combined with superior

performance relating to energy and the environment, seismic

safety, and comfort, will provide better value for the developer

and the homeowner in comparison with traditional

construction systems.


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5

Safety anddurabilityCodes and standards ensure wood buildings

are constructed for safety and durability

Wood frame construction has superiorseismic performance, even in the mostsevere earthquakes

Fire safety is assured by fire-rated, finishedassemblies, which have been fire-testedin China

Different climatic conditions requireappropriate detailing

Surveys in China demonstrate the durabilityof wood buildings

Design and construction practices arebacked by extensive research

53

Seismic safety


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Wood frame construction has superior seismic performance

Wood frame buildings are safer than concrete and masonry buildings in

areas with a high risk of earthquakes. They save lives and reduce the

cost of reconstruction.

Wood is strong, light and flexible. Wood buildings weigh less than

concrete buildings. This reduces loads on the structure, as well as the

danger of heavy weights falling from above. The flexibility of the wood

components allows the structure to deform and deflect momentarily in

response to seismic forces without breakage, collapse or disconnection.

Uplift and lateral loads are shared by the many wood members that

make up the framework, the wood structural panels fastened to them,

and the thousands of fasteners and connectors which tie the

components together. This structural redundancy is stronger than

predicted by conventional engineering analysis.

Additional measures can be taken in areas of greatest risk

In areas such as Sichuan, where severe earthquakes are likely, the

structural design of a standard wood frame can be enhanced simply and

inexpensively. Additional measures include braced walls, reinforced

connections between foundation and floor, and walls to roof, as well as

steel rod tie-downs that clamp the top wall to the foundation.

Engineered shear wall

Tongji University is actively involved in research to determine howwell wood construction performs under seismic conditions. We

tested a full scale, two storey wood building on our shake table,

simulating the most severe of earthquakes. The wood building

performed well and without problems.

Professor He Minjuan, Executive Dean of the College of

Continuing Education, Tongji University, March 2010

Above: Site of Beichuan middle school tragedy, Sichuan

Wood structural

panels of specific

grade and thickness

Specific stud species

Base shear

anchor bolts

Specific nail size and

spacing requirements

Hold down

anchors

f f


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A survey of wood frame construction in severe

earthquakes world-wide23

The survey covers wood frame buildings of all ages and provides

evidence of the superior safety of wood frame buildings in severe

earthquakes world-wide, including Japan and the United States.

A very high proportion of wood platform frame buildings survived

peak ground accelerations of 0.6 g and greater with no collapse or

serious structural damage. The resulting injuries and deaths were

few. There were very few specific failures, as for example from hillside

collapses. Virtually all modern wood frame buildings survived with

no visible damage.

Right: Three undamaged modern wood frame buildings (background) next toan older building ( foreground) whose ground floor has collapsed completely,Nishinomiya, Japan. Hyogo-ken Nanbu Earthquake, 1995.

Earthquake Richter Estimated number Total number Casualties in

Magnitude of wood platform frame of casualties wood platform

M houses strongly shaken frame houses

Alaska,

USA, 1964 8.4 - 130


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A survey of wood frame construction following the Wenchuan

earthquake, Sichuan24

A survey was conducted following the tragic earthquake of May 12, 2008.

The evidence showed that wood frame buildings had outperformedbuildings constructed from other materials. They suffered only minor

damage, while many brick infill walls collapsed and concrete buildings

suffered severe damage.

In Dujiangyan, 40 km NW of Chengdu, about 21 km from the epicentre of

the Wenchuan earthquake, many concrete and masonry structures were

seriously damaged. Many collapsed, including three school buildings.

Although not all the concrete and masonry collapsed, masonry infillwalls were severely damaged, causing potential danger to occupants.

Reconstruction is now underway in the Sichuan area. Chinese

authorities and specialists are working closely with Canadian and

European counterparts in the support of the rebuilding, which includes

houses, schools, and special facilities. These are permanent structures,

meeting all building code requirements.

This is a good example of how light wood frame construction is proving

to be cost-competitive in rural China, and responsive to local needs in

regions where annual incomes are low. Moreover, these newly

constructed wood-framed buildings are comfortable, energy-efficient,

with lower annual energy costs, and resistant to severe earthquakes.

56

Left: Wood-frame houses survived the Wenchuan earthquake with only minor damage,which could be easily repaired

Above: Beichuan, 100 km northwest of Chengdu, after the Wenchuan earthquake

The capability of a building to absorb seismic energy is a key

point, in addition to the performance of its structural system.

The damping of a steel structure is usually low. The damping of

a concrete and brick hybrid structure is high, but the dampingof WFC is even higher WFC has performed well in many

earthquakes and reduced casualties. There were a lot of

traditional buildings that collapsed in the Wenchuan earthquake

in May 2008, but wood frame buildings suffered no damage.

Prof. Lu Xilin, Dean of the Institute of Structural Engineering

and Disaster Reduction, Civil Engineering College,

Tongji University, March 2010

S i ti t th l t t h th b i f b ildi d


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Scientists use the latest research as the basis for building codes

International scientists have been working closely with Chinese experts

on seismic testing of wood frame building, using the shake test table

facility at Tongji University. They aim to provide technical data on seismic

performance. This will be used to develop building codes further, as

well as to establish seismic safety design guidelines for wood frame

construction and wood hybrid structures. The seismic intensities used

for testing were comparable to the extreme earthquakes of California. 25

Tests show multi-storey hybrid structures can survive the

most severe earthquakes

A full-scale, seven-storey mixed use condominium tower (six wood

frame storeys above a one-storey steel structure) was tested. Conducted

in Kobe, Japan, this was the largest full-scale earthquake test in the

world. The building was subjected to a simulated quake that was 180

per cent of the Northridge earthquake in California, and suffered no

significant damage. This demonstrates that even mid-rise wood

buildings can survive the most severe earthquakes. The test used

Japans massive E-Defense Shake Table, the largest shake table in

the world.

Above: Shake table test, Tongji University, Shanghai

Left: Seismic test of 6-storey wood frame building, Japan

Fire safety


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Buildings constructed from wood have to meet the same fire safety

codes as all other buildings

All countries take fire safety very seriously. In China, wood buildings

must meet the same fire codes and standards and safety performance

levels which apply to other forms of construction. In fact, when new

systems, such as wood frame, or glulam construction are first

introduced into a country like China, fire safety codes tend to be

overly cautious because of the lack of domestic experience with the

building system.

Building regulations in Europe and North America have been based on

function, rather than material, for many years. They stipulate what fire

load the structural assemblies and members must be able to withstand

and then require the designer to demonstrate that the stipulations can

be met.

Extensive research into the fire performance of structural wood

assemblies and materials used in wood frame construction is now well

underway in China. The Tianjin Fire Research Institute is working closely

with fire safety research specialists from Europe, Canada, and theUnited States. They are assessing fire safety relating to new

opportunities for wood construction in China and ensuring fire safety

codes are up to date with the latest research (see Chapter 7, Codes

and standards).

International fire safety statistics show no difference in losses between

countries which use wood extensively in construction and those which

do not. In North America and Europe, statistics show that people are

just as safe in a code-compliant wood frame house as they are in a

code-compliant house built of light frame steel, concrete, or masonry.

The limits for fire safety performance of large structural wood members

can be readily determined and incorporated into building design. As

wood burns in a predictable and controlled manner, it is possible to

estimate how much of the cross-section of a structural member will

remain unaffected by fire after a specified period of burning. Dimensions

can then be specified to ensure the unaffected part of the cross section

has the ability to bear the required load over the specified period.

Steel, on the other hand, loses all its load-bearing capacity at the

temperatures of a fully developed fire.

Top left: Tianjin Fire Research Institute (TFRI) fire test of structural glulam

column (in fire test furnace), 2007

Top right: TFRI fire test of wood frame wall assembly; thermo-couples attached togypsum plaster board cladding; (below) after the test, 2007


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The controlled charring rate of wood is clearly demonstrated when fire

testing for structural glue laminated timber. The charring rate is

0.7mm/min, and the remaining unaffected wood and its load bearing

capacity can be easily calculated as a function of time exposed to fire.

Fire safety depends on building assembly performance

In fact, fire safety performance in conventional wood frame construction

has little to do with the combustibility of the structural materials. It

relates to the finished building assemblies, like walls and roofs, whichare actually assessed in the tests. Wood framed assemblies are finished

on the interior with gypsum wall board panels. These have very low

combustibility ratings. Cavities are filled with non-combustible, mineral

fibre insulation. Testing requires these assemblies to be burned under

controlled conditions in fire research laboratories at very high

temperatures until they fail structurally. Wood framed structural wall

and roof assemblies are required to survive these high temperatures for

a minimum of one hour before structural failure.

Moreover, fire safety in low and medium density housing of all types

is rarely related to structural failure, but rather to the inhalation of

toxic smoke and gas. Fewer than 0.25 per cent of fire fatalities in these

buildings are caused by the collapse of roofs, walls, or floors. Non-

flammable surface materials, sprinkler systems and smoke detectorscan be used to ensure safety from toxic gases during the early stages

of a fire. Codes require that all buildings, including wood, be designed

and constructed to provide residents with a fast and easy exit in the

event of fire.

Top: Structural glulam beam after fire test. Wood surface chars at a predictablerate. The remaining uncharred wood retains its structural strength

Above: Wood burns at a predictable rate

Right: Gypsum wall board lining fulfilling fire requirements

We have been working closely with European and Canadian

research scientists and fire safety specialists to study the fire

resistance performance and safety aspects of wood buildings in

China. Extensive fire tests of wooden frame assemblies and

structural glulam have been carried out at TFRI national fire lab.

This research will assist us in determining appropriate, fire-safe

applications of wood products in construction assemblies, as well

as the codes that relate to these uses. We expect that this will lead

to new opportunities for wood in construction in China.

Mr. Ni Zhaopeng, Director, Tianjin Fire Research Institute;

Vice-Chairman of GB 50016 fire code committee, March 2010

Char layer

Pyrolysis zone

Normal wood


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Exterior wood products used for


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decks and other landscaping

projects are either made from

naturally durable wood species,such as the heartwood of China

fir, Western red cedar and yellow

cedar, or pressure treated with

chemical preservatives. Strict

environmental and health

regulations ensure these

chemicals are benign to humans

but resistant to insects and fungi.

Good design, workmanship, andmaintenance are also critical for

prolonging the service life of

outdoor wood products.

Modern wood frame construction has a good record of durability

Modern systems of wood frame construction also have a good record of

durability. This building type has a long history in Europe and North

America, and there are still houses standing from the original

developments. Many North American and European wood houses are

over a hundred years old. In 2005, 17 per cent of the US housing stock

was over 75 years old.

Wood frame is the most popular type of residential construction in North

America, even for areas like Hawaii and the Southern USA, where decay

and insect hazard are severe. Similar construction methods have also

been adopted in areas such as New Zealand, the UK, Japan, Korea and

China. Progress in design, material use and treatment, construction

techniques and maintenance have been made in recent decades to make

sure that wood buildings can endure indefinitely.

A survey on wood building service lives27

Buildings are rarely demolished because they are beyond repair, or have

become structurally unsound. Generally it is to make way for a larger or

more modern building. Simple to maintain and repair, wood buildings

are easily renovated to adapt to new requirements. At the end of their

economic service life, they can be demolished, with recovered materials

being reused, recycled or used as biomass energy.

Durability survey in China28

Forintek carried out a durability survey of wood frame houses in China

during 2006 and 2007. Results demonstrated that, with the durability

measures introduced into the relevant codes and standards in China,

including the Shanghai Technical Specification for Wood-Frame

Construction, wood construction in China is durable (See Chapter 7,Codes and standards).

0 10% 20% 30% 40% 50% 60%

Per cent of buildings

Above left: Liuhe Temple, Hangzhou, over 1,000 years old

Above right: 150 year old house, Canada - modern wood frame

construction has a good record of durability

0-25

26-50

51-75

76-100

100+

Distribution of 94 non-residential buildings by age class andstructural material

Ageclass

- years

ConcreteSteelWood


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Sustainable

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